President Polk sent John Slidell to Mexico City to try and purchase California and to resolve other conflicts. Mexico's new president, Jose Joaquin Herrera, refused meeting with John Slidell.
When there was no chance of diplomatic solution, Polk ordered General Zachary Taylor to lead troops across the Nueces River into territory claimed by the U.S. and Mexico. He wanted Mexican troops to fire the first shot, because then he could more easily win support for a war. Months later, news arrived that Taylor's men were attacked by a Mexican force. Four days later, the Senate and House both voted in favor of war.
Even before war with Mexico was declared, settlers in northern California had begun an uprising. The settlers had little trouble overcoming the Mexican presence in the territory.
On June 14, 1846, they declared California independent and renamed the region the Bear Flag Republic. Within a month, American naval forces arrived to occupy ports in San Francisco and San Diego and to claim the republic for the United States.
Mexico refused to surrender, despite loss or California and defeat in several battles. After a six-month campaign, Mexico's capital was captured.
Mexico's leaders signed the Treaty of Guadalupe Hidalgo after being defeated. Mexico gave the U.S. more than 500,000 square miles of territory, which are now California, Nevada, Utah, and most of Arizona and New Mexico, also parts of Colorado and Wyoming. Mexico accepted the Rio Grande as the southern border of Texas. In return, the U.S. paid Mexico $15 million and took over $3.25 million in debts the Mexican government owed to American citizens.
With Oregon and the former Mexican territories under the American flag, the dream of Manifest Destiny had been realized. The big question now was whether or not the new lands should allow slavery. This soon leads the country into another bloody conflict.
War With Mexico